This invention relates to phosphorus containing polymers, particularly to those copolymers of a cyclic phosphite and an epoxide.
Due to their thermal insulating character, good electrical resistance and resistance to moisture penetration, many thermoplastic and thermosettable compositions, particularly polyurethane compositions, are used extensively in the construction of refrigerators, truck panels and acoustical tile; as fibers or fabrics; as coatings; and in a wide variety of various other applications.
In many areas of application, the polyurethane compositions are required to exhibit flame resistant properties. Unfortunately, unmodified urethane polymers do not generally exhibit the desired fire resistance. For this reason, phosphorus, in the form of various phosphorus containing compounds and compositions, has been incorporated in the polyurethane compositions. In one method of incorporating phosphorus in a polyurethane composition, phosphorus compounds which are relatively unreactive towards the polyol and polyisocyanate reactants employed in preparing the urethane polymer such as the trialkyl phosphates, e.g., trimethyl phosphate, triethyl phosphate and tris(2-chloroethyl)-phosphate, are added to the reactant mixture or resulting polyurethane. Unfortunately, as such phosphorus compounds are merely physically incorporated within the polyurethane composition, they are subject to losses over a period of time by volatilization, the leaching action of solvents or water, and the like. Moreover, such phosphorus compounds often deleteriously affect the physical properties, e.g., dimensional stability, of the polyurethane composition.
In another method, the incorporation of phosphorus in the polyurethane composition comprises chemically bonding the phosphorus to the urethane polymer such as by preparing the urethane polymer using a suitably reactive phosphorus containing compound. For example, U.S. Pat. No. 3,474,047 discloses a fire-resistant polyurethane of the reaction product of a polyisocyanate, a phosphorus containing polyol prepared by reacting an alkylene oxide and a phosphorus containing acid and, optionally, other compounds reactive with the polyisocyanate such as polyester polyols and polyether polyols. Similarly, other urethane polymers prepared from other phosphorus containing polyols are described in U.S. Pat. Nos. 3,540,849; 3,989,652 and 3,142,651. Unfortunately, due to the presence of a large number of easily hydrolyzable phosphorus-oxygen bonds, the polyurethane compositions prepared from said compounds exhibit reduced hydrolytic stability.
To increase hydrolytic stability, urethane polymers prepared from various phosphorus containing compounds having fewer phosphorus-oxygen bonds have been proposed. For example, U.S. Pat. No. 3,445,405 proposes preparing the polyurethane from a polyisocyanate, a polyol and the condensation product of an alkylene oxide and tris(hydroxymethyl)phosphine oxide. Alternatively, U.S. Pat. No. 3,332,893 discloses a fire-resistant polyurethane can be prepared by combining a halogen containing hydroxyalkyl .alpha.-hydroxyalkyl phosphonate with a mixture of a polyol and polyisocyanate and subsequently polymerizing the resulting combination. Unfortunately, such phosphorus containing compounds are relatively expensive and difficult to prepare.
In view of the stated deficiencies of the prior art, it remains highly desirable to provide a readily prepared and relatively inexpensive phosphorus containing compound which is useful in the preparation of hydrolytically stable, thermoplastic and thermosettable compositions having increased resistance to fire.